System and method for re-publication of information in a network-based communication system

ABSTRACT

Methods, devices, and computer program products facilitate communications between two or more network entities that utilize Session Initiation Protocol. To this end, an Event State Compositor may force an Event Publication Agent to provide update information as deemed necessary by the Event State Compositor. The update of the publication information may be carried out by initiating an update triggering mechanism that is addressed to the Event State Compositor and comprises information that specifically identifies a particular publication. Such a triggering mechanism may be initiated when a predefined condition associated with the Event State Compositor&#39;s local policies is satisfied.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/104,667 filed on Oct. 10, 2008, which is incorporated herein byreference in its entirety.

FIELD OF INVENTION

The present invention relates generally to the enhancing thecommunication of information between various entities over a network.More particularly, the invention relates to methods, devices andcomputer program products for facilitating communications between twonetwork entities that utilize a protocol such as, for example, SessionInitiation Protocol.

BACKGROUND OF THE INVENTION

This section is intended to provide a background or context to theinvention that is recited in the claims. The description herein mayinclude concepts that could be pursued, but are not necessarily onesthat have been previously conceived or pursued. Therefore, unlessotherwise indicated herein, what is described in this section is notprior art to the description and claims in this application and is notadmitted to be prior art by inclusion in this section.

The Session Initiation Protocol (SIP) is a signaling protocol, widelyused for setting up and tearing down multimedia communication sessionssuch as voice and video calls over the Internet. Other applicationexamples of SIP include video conferencing, streaming multimediadistribution, instant messaging, presence information, online games andothers. The protocol can be used, for example, for creating, modifyingand terminating two-party (unicast) or multiparty (multicast) sessionsconsisting of one or more media streams. The SIP protocol is designed tobe independent of the underlying transport layer, and may be situated atthe session layer in the Open System Interconnection (OSI) model, and atthe application layer in the Transmission Control Protocol/InternetProtocol (TCP/IP) model. SIP has also been accepted as a 3rd GenerationPartnership Project (3GPP) signaling protocol and a permanent element ofthe IP Multimedia Subsystem (IMS) architecture for IP-based streamingmultimedia services in cellular systems.

SIP Requests are the codes used by SIP for communication. To complementthese Requests, there are SIP Responses, which generally indicatewhether a request has succeeded or failed, and in the latter case, whyit has failed. SIP User Agents (UAs) are the end-user devices, used tocreate and manage a SIP session. A SIP UA has two main components, theUser Agent Client (UAC), which sends messages and answers with SIPresponses, and the User Agent Server (UAS), which responds to SIPrequests sent by a peer. The SIP Events framework defines generalmechanisms for subscription to, and notification of, Events within SIPnetworks. It defines a Package as a specific instantiation of the Eventsmechanism for specific events. For example, Packages have been definedfor user Presence, Watcher information and other events.

According to SIP, Event State is defined as state information for aparticular resource that is associated to the particular Event Packageand an address-of-record. SIP further defines an Event Publication Agent(EPA) as the UAC that issues PUBLISH requests to publish event state,and an Event State Compositor (ESC), which is the UAS that processesPUBLISH requests and is responsible for compositing Event State into acomplete, composite event state of a resource. The act of an EPA sendinga PUBLISH request to an ESC to publish event state is referred to asPublication. PUBLISH allows SIP-compliant devices to publish Event Stateinformation, thus allowing them to publish any changes to the Stateinformation. SIP specifications further provide a mechanism for the EPAand the ESC to agree on an expiration interval that corresponds to theduration of validity of the published information. These and otherdetails regarding SIP Event State Publication may be found, for example,in Session Initiation Protocol Extension for Event State Publication(RFC 3903). Although an EPA can publish event state information and mayprovide updates to previously published information, there is currentlyno mechanism to allow an ESC to force an EPA to provide such updates ifsuch a need arises at an ESC. Failure to provide such an updatemechanism, may interfere with proper and efficient operation of ESC andproduce outdated information being provided to watchers monitoring theinformation.

SUMMARY OF THE INVENTION

The methods, apparatus and computer program products of the presentinvention enable an Event State Compositor (ESC) to force an EventPublication Agent (EPA) to provide update information as deemednecessary by the ESC. One aspect of the present invention relates to amethod, comprising receiving an initial publication from an eventpublication agent at an event state compositor, the publicationcomprising an expiration interval, sending a republication request totrigger an updated publication to the event publication agent prior toexpiration of the expiration interval, and receiving an updatedinformation from the event publication agent in response to therepublication request. In one embodiment, the initial publicationcomprises location information and the updated information comprisesupdated location information. In another embodiment, the initialpublication information comprises a contact information associated withthe event publication agent.

According to another embodiment of the present application, the contactinformation is located within at least one of a Contact header field ora Via header field. In a different embodiment, the Contact header fieldincludes a Globally Routable User Agent URI as defined indraft-ietf-sip-gruu-15. In a different embodiment, the sending istriggered in accordance with a predefined condition. In yet anotherembodiment, the predefined condition comprises at least one of anaddition of a new Watcher or a refreshing of a subscription of anexisting Watcher. In accordance with another embodiment of the presentapplication, the event publication agent is a presence source and theevent state compositor is a presence server, while in a differentembodiment, the republication request is carried out in accordance witha Session Internet Protocol (SIP) REFER request. In one variation, theREFER request comprises an entity tag for identification of apublication. In a different variation, a SIP-IF-Match header fieldcomprises the entity tag. In a different embodiment, the eventpublication agent includes an Allow:REFER header field in initialpublications. In yet a different embodiment, the updated informationcomprises at least one a refreshed, modified or removed information.

Another aspect of the present invention relates to a method, comprisingsending an initial publication from an event publication agent to one ormore event state compositors, the publication comprising an expirationinterval, receiving a republication request from at least one eventstate compositor prior to expiration of the expiration interval, andsending an updated information to the event state compositor in responseto the republication request. A different aspect of the presentinvention relates to a system, comprising sending an initial publicationfrom an event publication agent to one or more event state compositors,the publication comprising an expiration interval, receiving the initialpublication at an event state compositor, sending a republicationrequest from the event state compositor to the event publication agentprior to expiration of the expiration interval, receiving therepublication request at the event publication agent, sending an updatedinformation to the event state compositor in response to therepublication request, and receiving the updated information at theevent state compositor.

In yet another aspect of the present invention, a computer programproduct, embodied on a computer readable medium, is provided, comprisinga computer program for receiving an initial publication from an eventpublication agent at an event state compositor, the publicationcomprising an expiration interval, a computer program for sending arepublication request to the event publication agent prior to expirationof the expiration interval, and a computer program for receiving anupdated information from the event publication agent in response to therepublication request. Another aspect of the present invention relatesto a computer program product, embodied on a computer readable medium,comprising a computer program for sending an initial publication from anevent publication agent to one or more event state compositors, thepublication comprising an expiration interval, a computer program forreceiving a republication request from at least one event statecompositor prior to expiration of the expiration interval, and acomputer program for sending an updated information to the event statecompositor in response to the republication request.

Another aspect of the present invention relates to an apparatus,comprising a receiver configured to receive an initial publication froman event publication agent at an event state compositor, the publicationcomprising an expiration interval, and a transmitter configured to senta republication request to the event publication agent prior toexpiration of the expiration interval, wherein the receiver is furtheradapted to receive an updated information from the event publicationagent in response to the republication request. Still, another aspect ofthe present invention is related to an apparatus, comprising atransmitter configured to send an initial publication from an eventpublication agent to one or more event state compositors, thepublication comprising an expiration interval, and a receiver configuredto receive a republication request from at least one event statecompositor prior to expiration of the expiration interval, wherein thetransmitter is further configured to send an updated information to theevent state compositor in response to the republication request.

These and other advantages and features of various embodiments of thepresent invention, together with the organization and manner ofoperation thereof, will become apparent from the following detaileddescription when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described by referring to the attacheddrawings, in which:

FIG. 1 is a flow diagram block diagram illustrating the republication ofinformation in accordance with an example embodiment of the presentinvention;

FIG. 2 is an overview diagram of a system within which variousembodiments of the present invention may be implemented;

FIG. 3. illustrates a perspective view of an exemplary electronic devicewithin which various embodiments of the present invention may beimplemented; and

FIG. 4 illustrates an exemplary schematic representation of thecircuitry which may be included in the electronic device of FIG. 3.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, details and descriptions are set forth in order to provide athorough understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention may bepracticed in other embodiments that depart from these details anddescriptions.

As an entity responsible for aggregating state information frompotentially many sources, the ESC can be subject to considerable amountsof publication traffic. According to the SIP extension for event statepublication, event state that is published by an EPA may have a definedlifetime and may expire after a specified amount of time. An EPA isresponsible for refreshing its previously established publicationsbefore their expiration interval has elapsed. However, the expirationinterval for publications may be negotiated between the EPA and the ESC.In a one scenario, if the EPA offers a shorter expiration interval thanwhat the ESC local policy allows, the ESC may force the EPA to offer ahigher value. This task may be accomplished, for example, by using therequest/response header field identified as Min-Expires. The ability tonegotiate the expiration time ensures that the average time between twoconsecutive publications is kept at a certain minimum level. Furthermoreit allows the ESC to make sure that the refresh rate of publications donot cause an overload. In a second scenario, if the EPA offers a longerexpiration interval than what the ESC local policy allows, the ESC maylower the suggested lifetime of the publication. However, in typicalcases, the ESC simply accepts the EPA offered expiration value, allowingthe information to expire as suggested by the EPA. As a result, theagreed upon expiration interval may be relatively long due to efforts tocontrol the rate of publications.

In addition to a local policy for a minimum publication expiration time,the ESC may have another local policy containing conditions regardingwhen a particular type of information should be updated. An example ofthese additional considerations may be illustrated in terms of presenceinformation. Presence information is a status indicator that conveys theability and/or willingness of a potential communication partner, forexample a user, to communicate with other entities in a network. Auser's client provides presence information (e.g., presence state) via anetwork connection to a presence service, which is stored in whatconstitutes his personal availability record, also known as apresentity. The presentity can be made available for distribution toother users (called watchers) to convey its availability forcommunication. The Open Mobile Alliance (OMA), for example, has utilizedimplementations of the SIP protocol in the 3GPP IMS (IP MultimediaSubsystem) and 3GPP2 MMD (Multimedia Domain) for collecting anddisseminating presence information between the various Presence Sourcesand their watchers. In considering the rate of publications, a PresenceServer (i.e., an ESC) may have a condition to update the locationinformation of the presentity every time a new Watcher subscribes, orwhenever an existing Watcher refreshes its subscription. These and otheradditional conditions may thus affect the ESC's decision to negotiate anappropriate expiration interval with the EPA and/or require the receiptof update information at irregular times depending on whether or not apredefined condition is satisfied.

After an initial publication, the EPA has the complete responsibility tokeep the information refreshed, modified with new values or removedbefore the information expires. A problem arises in the existing systemsif the EPA fails to update the information at a regular interval and/orthe ESC has a local policy that requires an update when a certaincondition is met. According to an embodiment of the present invention, amechanism may be developed to allow the ESC to force the EPA to updatethe information under such circumstances.

Referring back to the previous example related to the presenceinformation, the Presence Server (i.e., the ESC) may have an agreed-uponone-hour expiration interval for the location information with thePresence Source (i.e., the EPA). In this example scenario, due therelatively long duration of the expiration interval, the probability ofhaving outdated location information within the existing presence ishigh. According to the existing methods, the Presence Source may or maynot refresh, modify or remove the location information before expirationof the one-hour interval. If the information is not updated, thelocation information simply expires. While the failure to update theinformation and/or expiration of the information may not be problematicfor existing watchers that have been monitoring the location of thepresentity, the Presence Server may find it necessary to sendnotifications regarding recent location information to newly subscribedwatchers, or those watchers which are just refreshing theirsubscriptions in accordance with their local policies.

According to an example embodiment of the present invention, thePresence Server may utilize a mechanism that triggers the PresenceSource to update the information. In response to such a trigger, thePresence Source may refresh the previous publication, modify it with newvalues or simply remove it. As such, the newly subscribed orre-subscribed watchers receive a recent value of the presentity'slocation instead of outdated values.

In one example embodiment, the ESC may use the SIP REFER method totrigger an update action. A REFER is a SIP extension, requesting thatthe recipient refer to a resource provided in the request. It provides amechanism for allowing the party sending the REFER to be notified of theoutcome of the referenced request. In accordance with an exampleembodiment of the present invention, the ESC may use the SIP REFERmethod to trigger the EPA to update a previous publication. To this end,the ESC may issue a REFER request, which in turn triggers the EPA toissue a non-initial PUBLISH, updating the previous publication. Theupdate may be a refresh, modify or remove operation.

It should be noted that while a REFER request may automatically createan implicit subscription, this subscription may not be desired by theESC. Accordingly, the ESC may opt to eliminate the implicit subscriptionthat is associated with a REFER request. As such, in one exampleembodiment, the automatic establishment of an event subscription andsubsequent notifications that are associated with a REFER request may beeliminated. This elimination, for example, may be carried out inaccordance with the procedures described in document “Suppression ofSession Initiation Protocol (SIP) REFER Method Implicit Subscription,”(RFC4488).

In order to send the REFER request, the ESC needs to be aware of theEPA's contact address. In accordance with an example embodiment of thepresent invention, an EPA may include a Contact header field for everyinitial PUBLISH request. The EPA may be running on user agent withseveral SIP applications. The EPA needs to make sure that the incomingREFER request is correctly routed to the right EPA instance. In order toachieve this should use a Globally Routable User Agent URI as the valuefor the Contact header field. The mechanisms to reserve a GloballyRoutable User Agent URI are defined in draft-ietf-sip-gruu-15. The ESCmay then use the SIP Uniform Resource Identifier (URI) from the Contactheader field to populate the Request-URI of the REFER request.Alternatively, or additionally, the contact information may be savedfrom the topmost Via header field, and the ESC may then acquire thecontact address from the topmost Via header to enable the sending of theREFER request. According to SIP, the Via header field indicates thetransport used for the transaction and identifies the location where theresponse is to be sent. The EPA should also advertise that it is capableto process a REFER request. This is achieved by including an‘Allow:REFER’ header field in every initial PUBLISH request.

Once an EPA receives a REFER request, it must determine whether or notthe REFER request is designated to trigger an update of an existingpublication. Furthermore, if the EPA is responsible for multiplepublications, it also needs to determine which publication is requestedto be updated. To this end, it may be possible to use Entity-Tags as away to reference a particular state of publication. In accordance withan example embodiment of the present invention, a new header field thatcomprises the identification information associated with the particularrequested publication may be included in the REFER request. In oneexample embodiment, a SIP-If-Match header field that includes anEntity-Tag referencing the requested publication may be included in theREFER request.

An exemplary embodiment of the present invention may be illustratedusing the OMA Session Initiation Protocol for Instant Messaging andPresence Leveraging Extensions (SIMPLE) Presence 2.0 service. FIG. 1 isan flow diagram that illustrates the various steps involved in obtainingupdated location information in accordance with an example embodiment ofthe present invention. FIG. 1 illustrates a Presence Source 100 (i.e.,an EPA) sending a PUBLISH 108, 110 request via the SIP/IP Core 104 to aPresence Server 106. The publication comprises information such as theexpiration interval with and exemplary duration of 3600 seconds, an‘Allow:REFER’ header field, as well as the location information asmessage payload. The initial PUBLISH 108, 110 request may include aContact header field including a Globally Routable User Agent URI whenthe Presence Server 106 (i.e., the ESC) initiates a trigger mechanism toobtain updated presence information. After the initial PUBLISH 108, 110,the Presence Server 106 reserves an entity-tag for the presenceinformation and sends acknowledgements 112, 114 to the Presence Source100. As illustrated in FIG. 1, at some point before the end ofexpiration interval, say 2000 seconds into the expiration interval, aWatcher 102 may SUBSCRIBE 116, 118 for an Event of Notification from thePresence Server 106. Upon acknowledgment 120, 122 by the Presence Server106, the Presence Server 106 may NOTIFY 124, 126 the Watcher 102, whichmay be followed by acknowledgement 128, 130 on the part of the Watcher102.

In order to further illustrate the various embodiment of the presentinvention, the Presence Server 106 may be configured with a local policythat requires an update of the previously published presence informationwhen a predefined condition is satisfied. According to an exampleembodiment of the present invention, such a condition may be satisfiedupon the subscription of a new watcher and/or when a watcher refreshesits existing subscription. In one example embodiment, an update of thelocation information may be triggered if the published information hasnot been updated for at least 30 minutes and the publication is notexpected to expire in the next five minutes. If all of the aboveconditions are met, the Presence Server may then initiate a mechanism,such as using the SIP REFER, to request an update of the locationinformation. The above-described local policy at the ESC may bedescribed using the following pseudo-code:

IF (Presence Information = Location Information) AND IF (PublicationExpiration Interval ≧ 1800 Seconds) AND IF (Remaining Duration inExpiration Interval ≧ 360 Seconds) THEN Send REFER to Presence Source.

Referring back to FIG. 1, when the triggering condition is satisfied,the Presence Server 106 may issue a REFER 132, 134 request to the URIthat may be present in the Contact header of the PUBLISH 108, 110request or the topmost Via header field of the PUBLISH 108, 110 request.The REFER 132, 134 request may include a “Refer-Sub: false” header fieldand a SIP-If-Match header field with the same entity-tag that wasspecified in the initial PUBLISH 108, 110. Upon acknowledgment 136, 138to the Presence Server 106, the Presence Source 100 may determinewhether or not the entity-tag associated with the SIP-If-Match headerfield matches a previous publication. In case of a match, the PresenceSource 100 may issues a new PUBLISH 140, 142 request to refresh, modifyor remove the previous publication. The Presence Server 106 may thenacknowledge 144, 146 the receipt of publication information.

FIG. 2 shows a system 10 in which various embodiments of the presentinvention can be utilized, comprising multiple communication devicesthat can communicate through one or more networks. The system 10 maycomprise any combination of wired or wireless networks including, butnot limited to, a mobile telephone network, a wireless Local AreaNetwork (LAN), a Bluetooth personal area network, an Ethernet LAN, atoken ring LAN, a wide area network, the Internet, etc. The system 10may include both wired and wireless communication devices.

For exemplification, the system 10 shown in FIG. 2 includes a mobiletelephone network 11 and the Internet 28. Connectivity to the Internet28 may include, but is not limited to, long range wireless connections,short range wireless connections, and various wired connectionsincluding, but not limited to, telephone lines, cable lines, powerlines, and the like.

The exemplary communication devices of the system 10 may include, butare not limited to, a electronic device 12, a combination personaldigital assistant (PDA0 and mobile telephone 14, a PDA 16, an integratedmessaging device (IMD) 18, a desktop computer 20, a notebook computer22, etc. The communication devices may be stationary or mobile as whencarried by an individual who is moving. The communication devices mayalso be located in a mode of transportation including, but not limitedto, an automobile, a truck, a taxi, a bus, a train, a boat, an airplane,a bicycle, a motorcycle, etc. Some or all of the communication devicesmay send and receive calls and messages and communicate with serviceproviders through a wireless connection 25 to a base station 24. Thebase station 24 may be connected to a network server 26 that allowscommunication between the mobile telephone network 11 and the Internet28. The system 10 may include additional communication devices andcommunication devices of different types.

The communication devices may communicate using various transmissiontechnologies including, but not limited to, Code Division MultipleAccess (CDMA), Global System for Mobile Communications (GSM), UniversalMobile Telecommunications System (UMTS), Time Division Multiple Access(TDMA), Frequency Division Multiple Access (FDMA), Transmission ControlProtocol/Internet Protocol (TCP/IP), Short Messaging Service (SMS),Multimedia Messaging Service (MMS), e-mail, Instant Messaging Service(IMS), Bluetooth, IEEE 802.11, etc. A communication device involved inimplementing various embodiments of the present invention maycommunicate using various media including, but not limited to, radio,infrared, laser, cable connection, and the like.

FIGS. 3 and 4 show one representative electronic device 12 within whichembodiments of the present invention may be implemented. It should beunderstood, however, that the present invention is not intended to belimited to one particular type of device. The electronic device 12 ofFIGS. 3 and 4 includes a housing 30, a display 32 in the form of aliquid crystal display, a keypad 34, a microphone 36, an ear-piece 38, abattery 40, an infrared port 42, an antenna 44, a smart card 46 in theform of a UICC according to one embodiment, a card reader 48, radiointerface circuitry 52, codec circuitry 54, a controller 56 and a memory58. Individual circuits and elements are all of a type well known in theart, for example in the Nokia range of mobile telephones.

The various embodiments described herein are described in the generalcontext of method steps or processes, which may be implemented in oneembodiment by a computer program product, embodied in acomputer-readable medium, including computer-executable instructions,such as program code, executed by computers in networked environments. Acomputer-readable medium may include removable and non-removable storagedevices including, but not limited to, Read Only Memory (ROM), RandomAccess Memory (RAM), compact discs (CDs), digital versatile discs (DVD),etc. Generally, program modules may include routines, programs, objects,components, data structures, etc. that perform particular tasks orimplement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of program code for executing steps of the methods disclosedherein. The particular sequence of such executable instructions orassociated data structures represents examples of corresponding acts forimplementing the functions described in such steps or processes.

The various embodiments described herein are described in the generalcontext of method steps or processes, which may be implemented in oneembodiment by a computer program product, embodied in acomputer-readable medium, including computer-executable instructions,such as program code, executed by computers in networked environments.Generally, program modules may include routines, programs, objects,components, data structures, etc. that perform particular tasks orimplement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of program code for executing steps of the methods disclosedherein. The particular sequence of such executable instructions orassociated data structures represents examples of corresponding acts forimplementing the functions described in such steps or processes.

The foregoing description of embodiments has been presented for purposesof illustration and description. The foregoing description is notintended to be exhaustive or to limit embodiments of the presentinvention to the precise form disclosed, and modifications andvariations are possible in light of the above teachings or may beacquired from practice of various embodiments. The embodiments discussedherein were chosen and described in order to explain the principles andthe nature of various embodiments and its practical application toenable one skilled in the art to utilize the present invention invarious embodiments and with various modifications as are suited to theparticular use contemplated. The features of the embodiments describedherein may be combined in all possible combinations of methods,apparatus, modules, systems, and computer program products.

What is claimed is:
 1. A method comprising: receiving an initialpublication from an Event Publication Agent at an Event StateCompositor, the publication comprising an expiration interval; sendingan acknowledgment to the Event Publication Agent, the acknowledgmentincluding an entity-tag for identification of publication; sending arepublication request from the Event State Compositor to the EventPublication Agent prior to expiration of the expiration interval; andreceiving an updated presence information from the Event PublicationAgent in response to the republication request, wherein therepublication request is carried out in accordance with a SessionInternet Protocol REFER request from the Event State Compositor, whereina SIP-IF-Match header field of the REFER request comprises the entitytar and the Event Publication Agent issues the updated presenceinformation when the entity tag of the SIP-IF-Match header field of theREFER request matches the entity tag of the acknowledgment, wherein acontact header field includes a Globally Routable User Agent UniformResource Identifier (GRUU).
 2. The method of claim 1, wherein theinitial publication comprises a contact information associated with theEvent Publication Agent.
 3. The method of claim 2, wherein the contactinformation is located within at least one of the Contact header fieldor a Via header field.
 4. The method of claim 1, wherein the sending istriggered in accordance with a predefined condition.
 5. The method ofclaim 4, wherein the predefined condition comprises at least one of anaddition of a new Watcher or a refreshing of a subscription of anexisting Watcher.
 6. A method, comprising: sending an initialpublication from an Event Publication Agent to one or more Event StateCompositors, the publication comprising an expiration interval;receiving an acknowledgment at the Event Publication Agent from at leastone Event State Compositor, the acknowledgment including an entity-tagfor identification of the publication; receiving a republication requestfrom the at least one Event State Compositor prior to expiration of theexpiration interval; and sending an updated presence information to theat least one Event State Compositor in response to the republicationrequest, wherein the republication request is carried out in accordancewith a Session Internet Protocol REFER request from the at least oneEvent State Compositor, wherein a SIP-IF-Match header field of the REFERrequest comprises the entity tag and the Event Publication Agent sendsthe updated presence information when the entity tag of the SIP-IF-Matchheader field of the REFER request matches the entity tag of theacknowledgment, wherein a contact header field includes a GloballyRoutable User Agent Uniform Resource Identifier (GRUU).
 7. The method ofclaim 6, wherein the initial publication comprises a contact informationassociated with the Event Publication Agent.
 8. The method of claim 7,wherein the contact information is located within at least one of theContact header field or a Via header field.
 9. The method of claim 6,wherein the sending is triggered in accordance with a predefinedcondition.
 10. The method of claim 9, wherein the predefined conditioncomprises at least one of an addition of a new Watcher or a refreshingof a subscription of an existing Watcher.
 11. An apparatus, comprising:a receiver configured to receive an initial publication from an EventPublication Agent at an Event State Compositor, the publicationcomprising an expiration interval; a transmitter configured to send anacknowledgment to the Event Publication Agent, the acknowledgmentincluding an entity-tag for identification of the publication; thetransmitter further configured to send a republication request to theEvent Publication Agent prior to expiration of the expiration interval,wherein the receiver is further adapted to receive an updated presenceinformation from the Event Publication Agent in response to therepublication request, wherein the republication request is carried outin accordance with a Session Internet Protocol REFER request from theEvent State Compositor, wherein a SIP-IF-Match header field of the REFERrequest comprises the entity tar and the Event Publication Agent issuesthe updated presence information when the entity tag of the SIP-IF-Matchheader field of the REFER request matches the entity tag of theacknowledgment, wherein a contact header field includes a GloballyRoutable User Agent Uniform Resource Identifier (GRUU).
 12. Theapparatus of claim 11, wherein the initial publication comprises acontact information associated with the Event Publication Agent.
 13. Theapparatus of claim 12, wherein the contact information is located withinat least one of the Contact header field or a Via header field.
 14. Theapparatus of claim 11, wherein the sending is triggered in accordancewith a predefined condition.
 15. The apparatus of claim 14, wherein thepredefined condition comprises at least one of an addition of a newWatcher or a refreshing of a subscription of an existing Watcher.
 16. Anapparatus, comprising: a transmitter configured to send an initialpublication from an Event Publication Agent to one or more Event StateCompositors, the publication comprising an expiration interval; areceiver configured to receive an acknowledgment at the EventPublication Agent from at least one Event State Compositor, theacknowledgment including an entity-tag for identification of thepublication; and the receiver further configured to receive arepublication request from the at least one Event State Compositor priorto expiration of the expiration interval, wherein the transmitter isfurther configured to send an updated presence information to the EventState Compositor in response to the republication request, wherein therepublication request is carried out in accordance with a SessionInternet Protocol REFER request from the at least one Event StateCompositor, wherein a SIP-IF-Match header field of the REFER requestcomprises the entity tag and the transmitter is configured to send theupdated presence information from the Event Publication Agent when theentity tag of the SIP-IF-Match header field of the REFER request matchesthe entity tag of the acknowledgment, wherein a contact header fieldincludes a Globally Routable User Agent Uniform Resource Identifier(GRUU).
 17. The apparatus of claim 16, wherein the initial publicationcomprises a contact information associated with the Event PublicationAgent.
 18. The apparatus of claim 17, wherein the contact information islocated within at least one of the Contact header field or a Via headerfield.
 19. The apparatus of claim 16, wherein the sending is triggeredin accordance with a predefined condition.
 20. The apparatus of claim19, wherein the predefined condition comprises at least one of anaddition of a new Watcher or a refreshing of a subscription of anexisting Watcher.